U.S. patent number 4,524,089 [Application Number 06/554,466] was granted by the patent office on 1985-06-18 for three-step plasma treatment of copper foils to enhance their laminate adhesion.
This patent grant is currently assigned to Olin Corporation. Invention is credited to Reza Haque, Edward F. Smith, III.
United States Patent |
4,524,089 |
Haque , et al. |
June 18, 1985 |
Three-step plasma treatment of copper foils to enhance their
laminate adhesion
Abstract
A three-step plasma treatment for improving the laminate
adhesion of metallic and non-metallic substrates is described. The
treatment comprises sequentially exposing the substrate to a first
plasma of oxygen gas, a second plasma of a hydrocarbon monomer gas
and a third plasma of oxygen gas. The process has particular
utility in forming polymeric films on one or more surfaces of
copper or copper alloy foils to be used in printed circuit
applications.
Inventors: |
Haque; Reza (Hamden, CT),
Smith, III; Edward F. (Madison, CT) |
Assignee: |
Olin Corporation (New Haven,
CT)
|
Family
ID: |
24213439 |
Appl.
No.: |
06/554,466 |
Filed: |
November 22, 1983 |
Current U.S.
Class: |
427/488;
427/255.6; 427/299; 427/327; 427/331; 427/377; 427/388.2;
427/388.5; 427/535; 427/575 |
Current CPC
Class: |
B05D
1/62 (20130101); B05D 3/142 (20130101); B05D
3/148 (20130101); H05K 3/382 (20130101); H05K
2203/095 (20130101); H05K 2201/0355 (20130101); B05D
2202/45 (20130101) |
Current International
Class: |
B05D
3/14 (20060101); B05D 7/24 (20060101); H05K
3/38 (20060101); B05D 003/06 () |
Field of
Search: |
;427/38,39,41,255.6,299,327,331,377,385.5,388.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Kominiak et al., Thin Solid Films 40, 141, (1977). .
Shen et al., "A Review of Recent Advances in Plasma
Polymerization", Plasma Polymerization, Amer. Chem. Soc. 1979,
1.varies.33..
|
Primary Examiner: Bueker; Richard
Attorney, Agent or Firm: Kelmachter; Barry L. Cohn; Howard
M. Weinstein; Paul
Claims
We claim:
1. A process for coating at least one surface of a substrate
material with an adherent polymeric film, said process
comprising:
forming a first plasma of predominantly oxygen gas in the vicinity
of said substrate material;
exposing said substrate material to said first plasma for a first
period of time;
forming a plasma of a hydrocarbon monomer gas in the vicinity of
said substrate material;
exposing said substrate material to said hydrocarbon monomer gas
plasma for a second period of time;
forming a second plasma of predominantly oxygen gas in the vicinity
of said substrate material; and
exposing said substrate material to said second oxygen plasma for a
third period of time.
2. The process of claim 1 further comprising:
providing an evacuable chamber containing two spaced-apart
electrodes; and
positioning said substrate material between said electrodes.
3. The process of claim 2 wherein each said plasma forming step
comprises:
introducing said gas into said chamber at a desired flow rate and
at a desired working pressure; and
applying a current at a desired frequency and a desired power level
to said electrodes.
4. The process of claim 3 further comprising:
said desired gas flow rate being in the range of about 0.5 sccm to
about 50 sccm;
said desired working pressure being in the range of about 5 mtorr
to about 100 mtorr; and
said desired frequency being in the range of about 10 kilohertz to
about 20 gigahertz.
5. The process of claim 4 further comprising:
said flow rate being in the range of about 5 sccm to about 10
sccm;
said desired working pressure being in the range of about 10 mtorr
to about 50 mtorr; and
said desired frequency being in the range of about 1 megahertz to
about 100 megahertz.
6. The process of claim 4 further comprising:
each said electrode having a surface area; and
said power level per said electrode area being in the range of
about 1 watt/in.sup.2 to about 14.8 watts/in.sup.2.
7. The process of claim 6 further comprising:
said power level per said electrode area being in the range of
about 4.9 watts/in.sup.2 to about 10 watts/in.sup.2.
8. The process of claim 4 further comprising:
said chamber with said electrodes defining a contained plasma
volume; and
said power level per said volume being in the range of about 0.17
watts/in.sup.3 to about 2.65 watts/in.sup.3.
9. The process of claim 8 further comprising:
said power level per said volume being in the range of about 0.88
watts/in.sup.3 to about 1.75 watts/in.sup.3.
10. The process of claim 2 further comprising:
evacuating said chamber to a desired base pressure prior to forming
each said plasma.
11. The process of claim 1 further comprising:
said substrate material comprising a metallic foil;
said first and third time periods being in the range of about 5
minutes to about 40 minutes; and
said second time period being in the range of about 0.5 minutes to
about 10 minutes.
12. The process of claim 11 further comprising:
said substrate material comprising a copper or copper alloy
foil;
said first and third time periods being in the range of about 10
minutes to about 20 minutes; and
said second time period being in the range of about 2.5 minutes to
about 5 minutes.
13. The process of claim 3 wherein the step of forming said
hydrocarbon monomer gas plasma further comprises:
introducing into said chamber at said desired flow rate and at said
desired working pressure a gas selected from the group consisting
of methane, propene and butadiene.
Description
This application is related to co-pending U.S. patent application
Ser. No. 554,465, filed on an even date herewith, to Haque et al.
for a One-Step Plasma Treatment of Copper Foils to Increase Their
Laminate Adhesion.
This application is directed to the production of treated copper
foil for use in electronic devices.
Printed circuit boards are currently used as the substrate
materials in a wide variety of electronic devices. Typically, these
boards are fabricated from a thin sheet of copper foil laminated to
either a fiberglass/epoxy hardboard or, in some cases, flexible
plastic substrates. During the latter stages of fabrication, the
majority of the copper foil is etched away to provide the desired
interconnecting circuitry between various components in an
electronics circuit design. With improvements in etching
technology, it is currently possible to achieve intercircuit line
spacing approaching 3 to 5 mils. Minimum line spacing is one of the
current technical limitations to continued miniaturization of
complex circuits. As the minimum line spacing is reduced, a higher
density component packing is permitted on a circuit board. Attempts
to further reduce the minimum line spacing have become limited by
the physical characteristics of the copper foil.
Generally, copper foil is produced by either electrodeposition or a
rolling technique. In both cases, the resultant surface of the foil
is not readily amenable to producing adequate bond strength after
lamination. As a result, all foil must be treated by an additional
electrochemical process to improve its bondability. The most common
electrolytic techniques currently used to improve the adhesion of
copper foils are directed to the production of dendritic surfaces
on the copper foil. The dendritic surfaces improve adhesion by
contributing to mechanical interlocking between the copper foil and
the substrate. However, the dendritic or roughened surfaces can for
specific applications unfavorably affect the performance
characteristics of the foil. For example, line spacing in the
selective etching of copper foils could be adversely affected.
Further, the degree of attenuation and the speed of transmission of
high frequency signals could also be adversely affected. In view of
this, a treatment that yields a copper foil with improved adhesion
without increasing the overall surface roughness is most
desirable.
Some interest in using substrates having polymer film coatings for
printed circuit applications has been expressed in the prior art.
Polymer coatings are particularly advantageous because they can
serve as capacitor dielectrics, insulators, and/or protective
layers. A variety of different approaches including sputtering and
ion implantation have been tried in an attempt to coat various
metallic and non-metallic substrate materials with polymer films.
U.S. Pat. Nos. 3,703,585 to Agnone et al. and 4,264,642 to Ferralli
illustrate some of these different approaches.
The technique for forming polymer films that has drawn the most
attention is the glow discharge plasma technique. It has been found
that polymer films formed using this technique have unique physical
properties and are relatively thin and substantially pinhole-free.
Most glow discharge plasma treatment techniques consist of placing
a substrate to be coated in a plasma in a surrounding chamber and
injecting a particular gas such as monomer into the chamber. The
type of gas injected into the chamber normally depends upon the
type of polymer coating to be deposited on the substrate. U.S. Pat.
Nos. 3,518,108 to Heiss, Jr. et al., 4,013,532 to Cormia et al.,
4,131,691 to Morley et al., 4,166,784 to Chapin et al., 4,170,662
to Weiss et al. and 4,226,896 to Coburn et al. and the article "A
Review of Recent Advances in Plasma Polymerization" by Mitchel Shen
et al., Plasma Polymerization, American Chemical Society, 1979
illustrate some of the plasma polymerization treatments that have
been used in the prior art.
While most glow discharge treatments inject a single gas into the
chamber in which the plasma is formed, it is also known to deposit
a polymer coating on a substrate by placing the substrate in a
plasma containing a mixture of gases. In U.S. Pat. No. 3,940,506 to
Heinecke, a process is described for selectively treating a surface
of an article comprising silicon in part and either silica or
silicon nitride in part by placing the article in a plasma
containing fluorine, carbon and a reducing species such as
trifluoromethane to deposit a fluoropolymer coating on the
article.
In yet another glow discharge plasma treatment process, an
amorphous continuous layer of SiO.sub.x is deposited onto a
substrate in a series of thin layers by glow discharge of an
organosilane and oxygen, interrupting the deposition as required,
and initiating a glow discharge in oxygen after each interruption
and prior to each subsequent deposition. U.S. Pat. No. 4,260,647 to
Wang et al. illustrates this type of approach.
In accordance with the present invention, a three-step plasma
treatment for depositing a polymer coating on a substrate material
to enhance its laminate adhesion is provided. The treatment
comprises sequentially exposing a substrate material to be coated
to a plasma of oxygen, a plasma of hydrocarbon monomer, and a
second plasma of oxygen. While the process of the present invention
has wide applicability, it has been found to have particular
utility in depositing relatively smooth polymeric films on copper
and copper alloy foils.
The process of the present invention is preferably performed by
inserting the substrate material to be coated into a chamber
containing two electrodes. The chamber is first evacuated to a
desired base pressure. After evacuation to the base pressure has
been completed, oxygen in gaseous form is introduced into the
chamber at a desired flow rate and the system is adjusted to a
desired working pressure. A suitable current at a desired frequency
and a desired power level are applied to the electrodes to create a
plasma of oxygen. After the substrate has been exposed to the
plasma for a desired time, the power is turned off, the gas flow is
shut off, and the chamber is evacuated back to the base pressure.
After the chamber has stabilized at the base pressure, a second gas
such as a hydrocarbon monomer is introduced into the chamber at a
desired flow rate and the system is adjusted to the desired working
pressure. A plasma with the second gas is then created by applying
current and power to the electrodes. Again, after the substrate has
been exposed to the second plasma for a desired period of time, the
power is turned off, the second gas flow is shut off, and the
chamber is evacuated back to the base pressure. Thereafter, the
substrate undergoes a third step wherein oxygen is again introduced
into the chamber at a desired flow rate and the system is again
adjusted to a desired working pressure and a plasma is created.
It is believed that during the first step or oxygen pretreatment,
the substrate material is primarily being cleaned. For example,
where the substrate material comprises a copper foil, residual
hydrocarbons, greasy materials and/or other contaminants are
believed to be removed from the surface on which the coating is to
be deposited. There may also be during this step some oxide
formation on the surface of the substrate. The second step deposits
the polymer film onto the substrate surface. It is believed that
during the third step of oxygen post-treatment some of the bonds in
the series forming the polymer film react with the oxygen to
provide polar bonding sites for improved adhesion effect.
The process of the present invention may be performed in a single
chamber in a batchwise manner or may be performed in a plurality of
chambers in a continuous or semi-continuous manner. After the
three-step treatment has been completed, the polymer coated
substrate material may be laminated to another material. For
example, the polymer coated substrate may be laminated to a
fiberglass epoxy substrate in the case of printed circuit boards or
to a polyimide in the case of flexible circuits.
It is an object of the present invention to provide a process for
treating a substrate material to improve its bondability.
It is a further object of the present invention to provide a
process as above for forming an adhesive polymeric coating on one
or more surfaces of a substrate material.
It is still a further object of the present invention to provide a
process as above for treating metal foil such as copper foil with a
polymer coating to improve its laminate adhesion.
These and other objects will become apparent from the following
description and drawings in which like reference numerals designate
like elements.
FIG. 1 is a schematic illustration of an apparatus that can be used
to perform the process of the present invention.
FIG. 2 is an exploded view of a portion of the apparatus of FIG.
1.
In accordance with the present invention, a process for depositing
a polymer film on at least one surface of a substrate material for
improving the laminate adhesion of the substrate material is
provided. While the following description describes the invention
in the context of forming a polymer film on copper foil, the
process of the present invention has wide applicability in treating
other metal and metal alloy substrates as well as treating
non-metallic substrates. Furthermore, while the invention will be
described as a batch operation, it can be used as part of a
continuous or semi-continuous operation.
Referring now to the Figures, the apparatus 10 includes a vacuum
chamber 12 in which the polymerization of the substrate material 14
takes place. In the vacuum chamber are two electrodes 16 and 18,
generally an anode 16 and a cathode 18. The electrodes 16 and 18
are both connected to an external power source 20 which may be
either any conventional DC source or any conventional AC source
known in the art. An AC source is preferred because films deposited
from DC glow discharge systems are generally poor and difficult to
reproduce. The electrodes 16 and 18 can be a screen, coil or plate
formed from any suitable electrical conductor such as stainless
steel, platinum or graphite. When an AC power source is used, the
electrodes 16 and 18 may also be formed from dielectric
materials.
In using an AC power supply, a current at a desired frequency and a
desired power level is supplied to the electrodes. Both the
frequency and the power level can be varied over a broad range as
is well known to those skilled in the art.
If desired, the anode 16 may be adjustable. Suitable means 22 for
adjusting the position of the anode relative to the cathode may be
provided. There may also be an indicator 24 for displaying the
separation between the anode and cathode. Generally, the electrodes
16 and 18 are spaced from about 2" to about 6" apart. In those
situations where the frequency is other than a radio frequency, one
or more magnets not shown may be mounted on the electrodes 16 and
18 to enhance the plasma.
The chamber 12 has an outlet 26 which permits evacuation of the
interior of the chamber. The outlet 26 may be connected to any
suitable conventional vacuum pump system (not shown) known in the
art for evacuating the chamber 12 to a desired base pressure.
The chamber 12 also has means 28 for introducing a gas or a mixture
of gases into the chamber interior. The gas supply means 28 may
comprise any suitable means known in the art such as a gas
distribution ring or one or more conduits opening into the chamber
interior. The gas supply means 28 may be connected through a
suitable ducting and valve arrangement to one or more gas sources
such as one or more gas containers not shown. If a plurality of gas
conduits are used in lieu of a gas distribution ring, each gas
conduit can be connected to an individual gas source. Any suitable
valve arrangement sufficient to permit regulation of the mass
and/or volume flow rate of each gas flowing into the chamber
interior may be provided as part of the gas supply means. If
desired, a pressure indicating device not shown such as a manometer
may be used to indicate the pressure level inside the chamber.
If desired, the chamber 12 may also be provided with means 29 for
heating the interior and/or means 30 for cooling the interior. The
heating means 29 may comprise any suitable means known in the art
such as a resistance coil. The cooling means 30 may also comprise
any suitable means known in the art such as water cooling loop. If
needed, means not shown for independently heating the substrate
material to be coated and/or either electrode 16 and 18 may also be
provided.
In performing the process of the present invention, the substrate
material 14 to be coated can be placed in one of a plurality of
positions. For example, it may be grounded to the anode, grounded
to the cathode or placed in the plasma in an ungrounded condition.
In a preferred technique for performing the process of the instant
invention, the substrate 14 is placed ungrounded between the
electrodes 16 and 18. Any suitable means known in the art may be
used to position the substrate 14 in the desired location. Prior to
being placed in the chamber 12, the substrate material may be
cleaned using any suitable cleaning treatment known in the art. Of
course, the type of cleaning treatment used will depend upon the
nature of the material forming the substrate and the type of
contaminants on the material.
The process is commenced by evacuating the chamber 12 to a desired
base pressure. It has been found that evacuating the chamber to an
initial pressure in the range of about 10.sup.-5 Torr to about
10.sup.-6 Torr is desirable. After the initial vacuum has been
established, oxygen is introduced into the chamber through the gas
supply means 28 at a flow rate in the range of about 0.5 standard
cubic centimeters per minute, hereinafter sccm, to about 50 sccm,
preferably from about 5 sccm to about 10 sccm. The oxygen gas is
introduced into the chamber interior at a desired working pressure
level which is not so low that there is a loss of discharge and not
so high that electrical instability and arcing occur. It is
desirable to have the pressure in the range of about 5 millitorr to
about 100 millitorr, preferably from about 10 millitorr to about 50
millitorr. After the oxygen gas has been introduced into the
chamber 12, electrical power and current are supplied to the
electrodes 16 and 18 by the external power source 20. Since the
power level needed to achieve the desired deposition
characteristics appears to be dependent upon the geometry of the
deposition equipment, it appears to be meaningful to describe the
power in terms of power per electrode area (watts/in.sup.2) and/or
power per contained plasma volume (watts/in.sup.3). The process of
the present invention may be carried out using a level of power per
electrode area in the range of about 1.00 watt/in.sup.2 to about
14.8 watts/in.sup.2 and/or a level of power per contained plasma
volume in the range of about 0.17 watts/in.sup.3 to about 2.65
watts/in.sup.3. Preferably, the level of power per electrode area
is in the range of about 4.9 watts/in.sup.2 to about 10
watts/in.sup.2 and/or the level of power per contained plasma
volume in the range of about 0.88 watts/in.sup.3 to about 1.75
watts/in.sup.3. The current to the electrodes 16 and 18 is
preferably supplied at a frequency in the range of 10 kilohertz to
about 20 gigahertz. Most preferably, the current frequency is
within the range of radio frequencies and is from about 1 megahertz
to about 100 megahertz. A frequency of about 13.56 MHz has been
found to be particularly useful. The power being supplied to the
electrodes 16 and 18 and the gas introduced into the chamber 12
create a plasma in the chamber 12.
The substrate 14 is exposed to the plasma of oxygen for a desired
time period. It has been found to be desirable to expose the
substrate during this first step to the oxygen plasma for a time
period in the range of at least about 5 minutes to about 40
minutes, perferably from about 10 minutes to about 20 minutes. It
is believed that during this oxygen pretreatment step, each surface
of the substrate 14 that is to be coated is being cleaned. For
example, where the substrate 14 comprises copper foil, residual
hydrocarbons, greasy materials and/or other contaminants are
believed to be removed from the exposed surface or surfaces of the
copper foil. While the substrate material is generally cleaned
prior to being placed in the chamber 12, this pretreatment step is
believed to remove some, if not all, residual contaminants. There
is also believed to be during this step some oxide formation on the
exposed surface or surfaces. However, these oxides are not believed
to be detrimental to the process as a whole.
After the substrate 14 has been exposed to the plasma for the
desired time period, the power is turned off, the oxygen flow is
stopped and the chamber 12 is evacuated back to the desired base
pressure. After the chamber has stabilized at the base pressure for
a desired period of time, a second gas is introduced through the
gas supply means 28 into the chamber 12. The second gas is
introduced at about the same flow rate and under the same working
pressure conditions as the oxygen in the pretreatment step. The
second gas may comprise any suitable monomer for producing a
desired polymeric film. When copper foil is being treated, it has
been found to be useful to introduce a hydrocarbon monomer into the
chamber 12. For example, the second gas may be either methane,
propene, or butadiene. After the second gas has been introduced
into the chamber under the desired pressure conditions, the power
is turned on as in the first step and a plasma is again created. It
has been found desirable to expose the substrate 14 to the monomer
gas plasma for a time period in the range of about 0.5 minutes to
about 10 minutes, most preferably from about 2.5 minutes to about 5
minutes. During this step, the polymer film is deposited on the
surface or surfaces of the substrate 14 to be coated. Generally, a
relatively pinhole-free polymer film having a thickness of about
100 .ANG. to about 1000 .ANG. will be deposited on the exposed
surface or surfaces. Where a hydrocarbon monomer is used as the
second gas, the polymer film composition should be a hydrocarbon
species. Here again, after the substrate has been exposed to the
plasma for the desired time period, the power and gas flow are shut
off and the chamber 12 is evacuated back to the base pressure.
After the chamber 12 has been stabilized at the based pressure for
a desired time period, oxygen is readmitted into the chamber 12 at
the same flow rate and under the same working pressure condition as
the previous steps. The power is again turned on and the substrate
is exposed to a second oxygen plasma. Here again, it has been found
to be desirable to expose the substrate with the polymeric film
coating to the plasma for a time period in the range of about 5
minutes to about 40 minutes, preferably from about 10 minutes to
about 20 minutes. During this post-treatment step, it is believed
that the polymeric film is made more amenable to later bonding by
the opening of the bonds in the species forming the polymeric film
and/or by the incorporation of oxygen into the bonds. For example,
where the polymer film is a hydrocarbon species, it is believed
that the post-treatment step takes away some of the hydrogen atoms
and opens up some of the bonds in the hydrocarbon link. After the
third step has been completed, the substrate material 14 with is
polymer film coating can be removed from the chamber 12.
After the polymer film coating has been plasma deposited onto the
surface or surfaces of the substrate material, the coated substrate
material may be laminated to a metallic or non-metallic material
not shown. For example, the coated substrate may be laminated to a
fiberglass/epoxy hardboard or a flexible plastic material such as a
polyimide. Any conventional laminating process known in the art,
including those that use adhesives, may be used to bond the coated
substrate to the metallic or non-metallic material.
To demonstrate the process of the present invention, the following
tests were performed.
EXAMPLE I
Samples of wrought copper alloy C11000 foil were first cleaned and
then placed in a vacuum chamber similar to the one shown in FIGS. 1
and 2. After each sample was placed in the vacuum chamber, the
chamber was evacuated to a background pressure of 10.sup.-5 Torr.
Thereafter, oxygen was introduced into the chamber at a flow rate
of about 5 sccm and at a working pressure of about 10 millitorr. A
power level of about 4.94 watts/in.sup.2 and about 0.88
watts/in.sup.3 was applied to the electrodes in the chamber and a
plasma was created. The current frequency was at about 13.56 MHz.
The samples were exposed to this plasma for time periods ranging
from about 5 minutes to about 20 minutes.
After the samples were exposed to the oxygen plasma, the chamber
was evacuated and stabilized back to the base pressure. Following
this, butadiene was introduced into the chamber at the same flow
rate and at the same working pressure. The same power level and
current frequency was applied and a butadiene plasma was created.
The copper foil samples were exposed to the butadiene plasma for
time periods ranging from about 2.5 minutes to about 15
minutes.
Thereafter, the chamber was evacuated and again stabilized back to
the base pressure. Oxygen at the same flow rate and at the same
working pressure as in the other steps was readmitted into the
chamber. Power at the same level and current at the same frequency
were applied to the electrodes to create an oxygen plasma. During
this step, the samples were exposed to the oxygen plasma for time
periods ranging from about 5 minutes to about 40 minutes.
Each copper sample treated by this procedure was then laminated to
FR-4 epoxy preimpregnated fiberglass cloth using the lamination
process recommended by the manufacturer for the manufacture of
rigid epoxy printed circuit boards. After lamination, the degree of
adhesion or peel strength was measured by using a peel test in
accordance with appropriate IPC standards. As shown in Table I, the
treated copper samples exhibited peel strength in the range of
about 4 to about 8.5 lbs/in width.
As a point of comparison, untreated wrought copper alloy C11000
foil samples were also laminated to FR-4 epoxy preimpregnated
fiberglass cloth and subjected to the same peel test. The untreated
wrought copper foils were found to have a peel strength in the
order of about 3 to about 4 lbs/in width.
TABLE I ______________________________________ Operational
Parameters Power 100 watts Gas flow 5 sccm Pressure 10 mtorr
Deposition Times (minutes) Initial C.sub.4 H.sub.6 Post-Treatment
Peel Strength O.sub.2 Deposition O.sub.2 (lb/in width)
______________________________________ (a) 10 5 20 6.0-8.5 (b) 5 5
20 5.0 (c) 20 5 20 7.5-8.0 (d) 10 2.5 20 6.0 (e) 10 10 20 4.0 (f)
10 15 20 4.0 (g) 10 5 10 7.5-8.0 (h) 10 5 5 5.0 (i) 10 5 40 5.0
______________________________________
EXAMPLE II
To further demonstrate the present invention, samples of copper
alloy C11000 foil were subjected as in Example I to an oxygen
plasma pretreatment, a butadiene plasma deposition treatment, and
an oxygen plasma post-treatment. The oxygen pretreatment was
applied for time periods in the range of about 7 minutes to about
10 minutes, the butadiene plasma deposition treatment was applied
for time periods in the range of about 3.5 to about 5 minutes and
the oxygen post-treatment was applied for time periods in the range
of about 14 minutes to about 20 minutes. The gas flow rate and the
pressure conditions in each step were the same as in Example I. The
power level during each step did differ from Example I in that it
was about 7.4 watts/in.sup.2 and about 1.33 watts/in.sup.3.
As in Example I, the treated samples were laminated to FR-4 epoxy
preimpregnated fiberglass cloth and subjected to a peel test. As
can be seen from Table II, the samples exposed to the butadiene
plasma deposition treatment for a time period of about 3.5 minutes
exhibited a peel strength in the range of about 5 to about 6.5
lbs./inch width whereas the sample exposed to the butadiene
deposition for 5 minutes only exhibited a peel strength of about 1
lb./inch width. While it is not clear why the latter sample
exhibited a significant loss of peel strength, the data does
suggest that increased power shortens the allowable period for the
polymer film deposition step.
TABLE II ______________________________________ Operational
Conditions Power 150 watts Gas flow 5 sccm Pressure 10 mtorr
O.sub.2 C.sub.4 H.sub.6 O.sub.2 Post- Pretreat Deposition Treatment
Peel Strength (minutes) (minutes) (minutes) (lb/in width)
______________________________________ (a) 10 3.5 14 6.5 (b) 7 3.5
20 5.0 (c) 7 5.0 14 1.0 ______________________________________
While the present invention has been described in terms of a
particular plasma deposition equipment, it should be generally
applicable to a wide range of such equipment. It is believed,
however, that the operational ranges described above for the
various processing variables may be strongly dependent upon the
specific geometry of the deposition equipment. Therefore, with a
change in equipment, results similar to those described
hereinbefore may be obtained outside the aforementioned processing
limits.
While particular hydrocarbon monomers have been described to
deposit a polymer film, it is believed that similar results would
be obtained with virtually any straight chain hydrocarbon,
independent of the C to C bond structure, i.e. single, double or
triple bonds, or chain length.
While the invention has been illustrated in the context of applying
a hydrocarbon polymer film to a copper substrate, it is believed
that similar polymeric films for improving laminate adhesion could
be deposited on substrates formed from copper alloys, other metals
and metal alloys and non-metallic materials such as silica using
the process of the present invention.
While the invention has been described in terms of a bathwise
technique, the process may also be used in a continuous or
semi-continuous operation. If desired, each step of the three-step
process of the present invention could be performed in a separate
vacuum chamber. The only limitation to continuous and/or
semi-continuous operations would be not to expose the substrate to
be coated to the atmosphere between the various steps of the
process. It should be recognized that by performing each step in a
separate chamber, it may not be necessary to evacuate each chamber
back to the base pressure before subjecting the substrate to the
next step of the process.
Depending upon the position of the substrate relative to the
electrodes, the polymeric film coating may be deposited on either
one surface or a plurality of surfaces of the substrate. It it is
desired to deposit the polymeric coating on only one side while the
substrate is in an ungrounded condition, two substrates can be
placed adjacent one another so that the adjacent substrate faces
are not coated.
The patents and article set forth in this specification are
intended to be incorporated by reference herein.
It is apparent that there has been provided in accordance with this
invention a three-step plasma treatment of copper foils to enhance
their laminate adhesion which fully satisfies the objects, means,
and advantages set forth hereinbefore. While the invention has been
described in combination with specific embodiments thereof, it is
evident that many alternatives, modifications, and variations will
be apparent to those skilled in the art in light of the foregoing
description. Accordingly, it is intended to embrace all such
alternatives, modifications, and variations as fall within the
spirit and broad scope of the appended claims.
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